Variable transformer



July 21, 1959 w. H LAURIE 2,896,179

VARIABLE TRANSFORMER Filed Nov. 23, 1956 3 Sheets-Sheet 1 1979 01? NE Y61 INVENTOR. W17 7 14/77 if L dun/6 July 21, 1959 w. H.4LAURIE {VARIABLETRANSFORMER Filed Nov. 23, 1956 3 Sheets-Sheet 2 56a 59 INVENTOR. aWZZZmm H. Laurie ATTORNEYS y 21,1959 w. H. LAURIE 2,896,179

VARIABLE TRANSFORMER s Sheets-Sheet s Filed Nov. 25 1956 102 INVENTOR'Wallm/zzji ,Zaume ATTORNEYS VARIABLE TRANSFORMER William H. Laurie,Plainville, Conn., assignor to The Superior Electric 00., Bristol,C'onn., a corporation of Connecticut Application November 23, 1956,Serial No. 623,908

6 Claims. (Cl. 336-141) The present invention relates to a variabletransformer and, more particularly, to such a device having a windingprovided with a conducting surface.

An object of the present invention is to provide in a variabletransformer having a stationary winding with a collecting surface and abrush, a brush actuating mechanism which causes the brush to engage onlyone turn of the winding at a time throughout the limits of travel of thebrush.

Another object of the present invention is to provide a brush actuatingmechanism which causes the brush to move in a helical path.

A further object of the instant invention is to provide in a variabletransformer having a helical winding, a brush actuating mechanism whichmoves the brush in a helix having the same helical dimensions as thewinding.

An object of the present invention is to provide a brush movingmechanism which is extremely simple in operation, reliable in use overan extended period, economical to manufacture and very compact.

A further object of the present invention is the provision of a variabletransformer having a winding that remains stationary and a brushrotatable thereabout in which a brush actuating mechanism is soconstructed and arranged as to prevent circulating currents from beinginduced into the mechanism.

In application, Serial No. 467,781, filed November 9, 1954, entitledVoltage Regulating Apparatus, by Gustav O. Fredrickson, now abandoned,there is disclosed a variable transformer which is an autotransformer inwhich a helical winding is caused to rotate and a brush is movedparallel to the axis of the winding to effectuate the desiredtransformation of the input voltage. However, though satisfactory, sucha device necessitated a complex bearing structure to support the Windingfor rotation and such structure as heretofore constructed did notprovide for a sufiiciently reliable usage over an extended period. Alsoa re-entrant ring Was required for each tap in the winding in additionto a ring for each connection to the ends of the winding and thereby thedevice was limited as to the plurality of voltages for which it couldserve.

It is a further object of the above invention to provide a variableautotransformer in which only a simple hearing structure is requiredthat is reliable in use over an manually or by a motor and the brush iscarried along a circular path about the periphery of the stationarycoil.

United States Patent able with the winding. One of the rings is rotatedeither 2,896,179 Patented July 21, 1959 Also carried by the rings is atleast one screw rod extending therebetween and the brush has a threadedaperture mating with the screw rod. The threads of the rod have the samepitch or length of axial movement per revolution as the distance betweeneach convolution of the coil. A third rotatable ring is mounted adjacentone of the other rings for rotation with the axis of the third ringeccentric to the other rings. A link connects a pin carried by the thirdring with the screw. Accordingly, as the brush is rotated about theperiphery of the winding by the pair of spaced-apart rings the screw rodis held against rotation about its own axis by the connecting link beingfastened to the pin on the eccentrically mounted third ring which causesthe brush to move one thread on the screw for each revolution that itmakes about the coil. Thus, the brush is moved along the axis of thecoil and about the periphery thereof in a helical path Which correspondsto the helically wound coil.

A further feature of the invention resides in preventing the inductionof circulating currents in the rings and other portions of theautotransformer which encircle the leg of the core by forming someportions of nonmagnetic, non-conducting material and other portions withinsulating segments to avoid a closed conducting loop.

While the instant embodiment of the invention describes anautotransformer, it is within the scope of the invention to utilize atransformer having primary and secondary windings or a resistor in whichno magnetic core is present.

Other features and advantages of the invention will be apparent from thespecification and claims when considered in connection with the drawingin which:

Figure 1 is an elevation of a variable autotransformer, shown partly insection.

Fig. 2 is a view taken on the line 22 of Fig. 1.

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 1. I

Fig. 4 is an enlarged longitudinal section.

Fig. 5 is an elevation of the brushes and brush holder.

Fig. 6 is an enlarged detail taken on the line 66 of Fig. 5.

Fig. 7 is a fragmentary perspective View of the reentrant ring and itsassociated core.

Fig. 8 is a fragmentary perspective illustration of a portion of there-entrant ring.

Fig. 9 illustrates one form of the core of the re-entrant ring.

As shown in the drawing, Fig. 1 in particular, the autotransformer inthe instant embodiment in which the brush-moving mechanism isincorporated, is generally indicated by the reference numeral 10. Ahollow cylindrical tube 11 is provided which may be formed of insulatingmaterial, such as a phenolic compound, and a conducting winding 12. ishelically wound on the exterior surface of the tube 1-1. At present, it,is preferred to form the tube with a helical groove and form the Wirein the shape of a helix and then snap the wire into the groove. At leastthe outside surface of the winding 12 is bare to provide a collectingsurface. A rectangular magnetic core 13, preferably formed of laminatedmaterial, has one leg portion extending through the interior of the tube11 so that the winding 12 circumscribes this leg portion. A pair ofchannels 14, one of each of which is positioned against each verticalside of the bottom leg of the core 13, and are clamped together with thecore therebetween as by a nut and bolt 14a. The upper edges of thechannels 14 have apertures through which bolts 14b pass to be threadedinto a support plate or base 15 of the tube 1 1. In order to provide forconduc tion of the current from the commutating surface of the 3 winding12, a brush holder 16, having brushes 17, is mounted for rotation aboutthe periphery of the tube 11.

The mechanism for actuating the brushes is such that it will cause thebrushes to be rotated about the winding and also be moved axially of thewinding the distance between one turn and the next for each revolutionof the brush about the winding. The brush in its movement from one endof the winding to the other is constantly in contact with only a portionof one turn of the winding since it moves in a helix having a pitch thesame as the winding and thus there is prevented any short-circuiting ofa turn by the brush being in contact simultaneously with two adjacentturns.

This brush actuating mechanism includes a ring gear 18, located adjacentthe bottom end of the winding, and an upper ring 19, mounted adjacentthe upper end of the winding with both rings being mounted for rotationabout the winding. Spacer rods 20 extend between the two rings and movewith them relative to the stationary tube 11. A pinion gear 22 isprovided, which meshes with teeth 21 formed on the external periphery ofthe ring gear 13 to rotate the rings, and means are provided foroperating the pinion gear. In the instant embodiment this means isillustrated simply as a handle 23, however, other driving means such asa motor may be employed if desired.

Also extending between the two rings 18 and 19 are a pair of threadedscrew rods 24 and a pair of counterbalancing rods 25, these beingequispaced about the rings. Each of the screw rods 24 andcounterbalancing rods 25 has a lower end portion which projects throughand beneath the ring gear 18 and to each end portion of which there isfastened a link 27. Each link is connected to a corresponding pin 28 andthe pins 28 are fastened onto a ring 29. The ring 29 is mounted forrotation about an axis eccentric to the axis of the rings 18 and 19.

Accordingly, as the pinion 22 drives the ring gear 18, the rings 18, 19and 29 rotate together about the stationary tube 11 and also the screwrods 24 and counterbalancing rods 25 will be rotated therewith about thetube 11. By reason of the eccentric mounting of the ring 29 and theconnection to the screw rods 24 by means of the link 27 and the pin 28,the screw rod will be held stationary against rotative movement aboutits longitudinal axis. Also, the counterbalancing rods 25 are heldstationary about their longitudinal axes. Accordingly, there will berelative rotation between the rings 18 and 19 and the rods 25 and 24 asthe rings are rotated.

The brush holder 16 is carried by the screw rods 24 and has on each endportion a bushing 30 which screws into a threaded aperture 31 formed ineach end portion on the brush holder 16. The bushing is externallythreaded as at 32, and also is internally threaded as at 33.Intermediate the external threads a peripheral groove 35 is formedagainst which set screws 34 abut to hold the bushing stationary withrespect to the holder. The threads of the screw rods 24 mate with theinterior threads 33 of the bushing and, thus, as the brush holder movesabout the periphery of the winding 12 for each revolution that it isrotated, it advances the holder one screw thread with respect to thescrew rod. The screw threads have the same pitch as the helical winding12 and are shown as a double thread. The internal threads of the bushingare preferably square and the external threads are preferably acme inorder to provide for initially aligning the brush holder with respect tothe winding though other combinations of threads may be employedprovided they have different pitches to permit such adjustment.

Referring to the other views, Fig. 4 in particular, in which there isshown the details of construction of the instant embodiment of theinvention, the inner periphery of the ring gear 18 has a flanged portion36 which fits within a raceway 37 carrying ball bearings 38. The raceway37 is formed of two mating portions 39 and 40 held together as by screws41. Lips 42 abut the flange 36 to hold the gear in the raceway and toprovide a dust cover. The ring gear 18 is provided with an aperture 43into which is fitted a ball bearing 44 held in place as by a C-ring 45and an abutment 45a. The screw rod 24 has an unthreaded portion 47consisting of an upper portion 47a, an intermediate portion 47b, and alower square portion 470, with each portion being successively reducedin crosssection. The flange formed between the portions 47a and 47brests on an edge of the inner raceway of the ball bearing 44 while theportion 47b abuts the sides of the ball bearing. A bushing 46 alsocircumscribes the portion 47b. The extreme tip of the rod is threaded asat 49 for cooperation with a nut 50. The link 27 has a square aperture51 into which the portion 470 fits and the link, at its other endportion, contains another aperture into which the pin 28 fits. The pin28 is fastened to the eccentric ring 29 by means of a nut 53 screwingonto a threaded portion 52 of the pin 28. The effective length of thelinks between the rod 24 and the pin 28 is substantially equal to theamount of eccentricity between the rings 18 and 19 and the ring 29.

The eccentric ring 29 on its inner periphery has a flange 54 mounted forengagement with balls 55, the balls being part of a ball bearing.Holding the balls in place are two mating portions 56 which havedepending lips 56a to prevent shifting of the ring 29 and to provide adust cover. Screws 58 hold the mating portions 56 together. A circularend plate or base 59 is mounted adjacent the portion 56 and screws 60pass through the end plate 59, the two mating portions 56 and the twomating portions 39 and 40, and thread into the tube 11 to thus maintainthe parts securely connected to the tube 11. The tube 11 is formed witha step 61 which abuts the mating portion 37 to form a surface againstwhich the portions may be forced by the screws to be held in place.

The upper ring 19 has an aperture 62 into which a ball bearing 63 ispositioned. The upper end of the screw rod 24 fits within the ballbearing. The inner periphery of the ring 19 has a flange 65 which fitsinto a ball bearing raceway for engagement with ball bearings 66. Theraceway is formed to have a center portion 67 and upper and lower lipportions 68 and 69. A spacer ring 70 abuts the upper portion 68 and ontop of the spacer ring is mounted a clamping block 71 for holding inplace an annular re-entrant ring 72. The parts are clamped to the tube11 as by screws 73 threading into the tube 11 and a step 74 formed inthe tube 11.

Referring to Fig. 1, the spacer rods 20 are connected to the ring gear18 and the upper ring 19 by screws 75. Since these rods remainstationary with respect to the rings 18 and 19, there is no necessityfor providing for a rotatable connection.

However, the counterbalancing rods 25, since they rotate with respect tothe rings, pass through bushings 76 formed in the upper ring 19 and thering gear 18.

Shown in Figs. 3, 4 and 5 are details of the brush holder 16. The carbonbrushes 17 are forced against the helical winding 12 by means of aplurality of springs 77, there being one spring for each brush. Eachbrush consists of a carbon portion 78a fixed to a copper brush retainer78. The brushes are positioned in slots formed in the holder 16 and aplate 79 is fastened to the holder to maintain the brushes therein. Theplate 79 is preferably formed of copper. A lead 81 is connected betweeneach brush retainer 78 and the copper plate 79 as by soldering to permitconduction of electric current. The

brush holder 16 is arcuate and the brushes are inclined on a line havingthe same pitch as the turns of'the winding 12.

The brush holder holding the brushes is preferably formed of threeportions, the main portion 16a, a slot forming portion 82 and the plate79. The sides of the slot forming member 82 and the adjacent sides ofthe main portion 16a of the holder have a tongue and groove connection84. As shown in Fig. 3, the spacer rods 20 pass through the holder 16 atthe junction. of the tongue and groove connection 84. Each tongue hasfixed therein a carbon brush 82a which rides on the corresponding spacerrod 20. The brushes 82a are so positioned that the reaction force of thesprings 77 causes the brushes 82a to bear against the spacer rods. Whenit is desired to change the brushes 17 only the plate 79 has to beremoved. To change the brushes 82a only the two spacer rods have to beremoved in order to provide for the insertion of a new slot formingmember 82. Accordingly, the need to readjust the position of the brushholder with respect to the screw rods 24 whenever brushes are changed isobviated by the above construction.

As shown in Fig. l, a lead 85 extends into the interior of the tube 11to connect 'with the lower end of the winding 12 and another lead 86 isconnected to the upper end of the winding. Another lead 87 is connectedas by soldering to the stationary re-entrant ring 72. The leads, ifdesired, may be connected to a terminal box (not shown). There is alsoshown a plurality of leads which serve as taps to the winding 12.

In order to transmit the current from the brushes 17 to the re-entrantring 72 the upper ring 19 has a conducting plate 90 which engages theend portions of the two spacer rods. A lead 92 connects the plate 90 toa brush retainer 94 carrying a brush 95. A spring 96 biases the brushretainer 94 carrying the brush 95 upward into engagement with there-entrant ring 72. The plate 90 is formed with lips 97 which limit theoutward movement of the retainer 94 and brush. Accordingly, current canbe conducted from the brushes 17 to the brush retainers 78 and then bythe copper lead 81 to the plate 79. Thence, it is conducted by the slotforming portion 82 to the brushes 82a and hence to the two spacer rods20. The spacer rods conduct the current to the plate 90 and the currentcan then pass to the brush 95, the reentrant ring 72, and to the outputlead 87.

The re-entrant ring in the present embodiment is similar to thatdisclosed in application, Serial No. 467,7 81, above-mentioned and nowabandoned, in that it is formed with a plurality of broken annularrings. The exterior surface of the ring is composed of a plurality of U-shaped members 98 having angled ends with fiat connecting links 99extending from the end of one leg of one member to the opposite end ofthe leg of the adjacent member. The links 99 constitute a conductingsurface on which the brush 95 rides. More specifically, shown in Figs. 7and 8 are two views of the re-entrant ring which were taken from theabove-noted application, with the connecting links 99, however, beingdisposed in a radial plane. It will be appreciated that the members 98and 99 form a continuous toroidal winding. The re-entrant ring has aparamagnetic core 100 formed of flat annular stampings 101 ofparamagnetic material with each interrupted by a chordally disposed slot102, with the slots on adjacent stampings being preferably incircumferentially spaced relation. These stampings are axially spaced byintervening insulating strips 103 and an insulating cover 104 insulatesthe toroidal winding from the core. Thus the re-entrant ring is composedof an annular paramagnetic core formed of ferromagnetic material havinga continuous toroidal winding wound thereabout.

The rings 18, 19 and 29, the tube 11, and the base 15 encircle the legof the core 13 and thus would be subject to the magnetic influence ofthe core which would cause induced currents to be set up in the parts.However, according to the present invention, the parts are formed of anon-magnetic, non-conducting material such as a phenolic compound. Theballs of bearings 38, 55 and 66 are of steel but are maintained in adiscontinuous 6 ring by a plastic ball retainer ring. There is thuscurrent induced only in the winding and in the re-entrant ring.

There has been disclosed a variable autotransformer in which there isprovided a simple, eflicient and extremely compact mechanism for causinga brush to move in a helical path so as to be in contact with only oneturn of the winding at a time. The mechanism is such that it willfunction reliably and troublefree over a long period. In addition, anyannular portion except for the Winding and the re-entrant ring whichencircle the magnetic core is formed to prevent the inducing of circularcurrents, though obviously when the brush actuating mechanism isutilized Without a magnetic core as in a resistor, the need forprevention of the induced circular currents is obviated.

Variations and modifications may be made within the scope of the claimsand portions of the improvements may be used without others.

I claim:

1. In combination with a variable transformer having a helical windingand a brush operable on the winding, a brush actuating mechanism formoving the brush in a helical path to engage only one turn of thewinding at a time comprising a pair of spaced-apart ring members mountedfor rotation, a screw rod extending between the members and having apitch substantially equal to the pitch of the winding, a brush carrierformed with a threaded aperture through which the screw rod is threaded,a third ring mounted for rotation on an axis eccentric to the axis ofthe other rings, a pin carried by the third ring and a link connectedbetween the pin and the screw rod for maintaining the screw rodstationary on its longitudinal axis as it is rotated about the winding,and means for rotating the rings, whereby the brush carrier is caused tomove in a helical path in contact with only one turn of the winding at atime throughout its limits of movement.

2. The invention as defined in claim 1 in which the transformer has amagnetic core and the rings encircle a portion of the core, said ringsbeing formed to have at least a portion thereof of non-conductingmaterial whereby induced currents are prevented.

3. A mechanism for causing a brush to traverse a helically wound coil incontact at all times with only one turn of the coil comprising a pair ofspaced-apart rings, means on one of the rings to provide rotation of therings, at least one screw rod connected to the two rings and extendingtherebetween, a brush holder positioned between the two rings and havinga threaded aperture through which the screw is threaded, a third ringmounted for rotation on an axis eccentric to the axis of the otherrings, a pin carried by the third ring, and a link connected between.the pin and the screw rod, said link being effectively equal in lengthto the amount of eccentricity thereby preventing rotation of the screwrod about its own axis as it is rotated about the axis of the ringswhereby the brush is caused to move in a helical path upon rotation ofthe rings.

4. A variable autotransformer comprising a closed magnetic core, a tubeformed of insulating material encircling at least a portion of the core,a helical winding positioned on the exterior of the tube, a ring mountedon the tube for rotation adjacent each end of the tube, a spacer rodextending between the rings, a screw rod having a pitch substantiallyequal to the pitch of the winding extending between the rings, a brushcarrier formed with an aperture through which the spacer rod extends anda threaded aperture through which the screw rod is threaded, a brushcarried by the brush carrier for engagement with the 'winding, springmeans for biasing the brush into engagement with the winding and forbiasing the brush carrier into sliding electrical engagement with thespacer rod, a third ring mounted for rotation on the tube on an axiseccentric to the axis of the other rings, a pin carried by the thirdring and a link connected between the pin and the screw rod, means forrotating the three rings to cause the brush to be moved in a helicalpath to be in contact with only one turn of the Winding at a timethroughout its length'of movement, said three rings being'formed ofnon-conducting material, a stationary re-entrant ring mounted adjacentthe end of the tube, a brush carried by one of the first two mentionedrings and in electrical engagement with the re-entrant ring, and meanselectrically connecting the first named brush to the brush carrier andthe spacer rod to the last named brush whereby electrical current may beconducted from the winding to the re-entrant ring.

5. An adjustable autotransformer for producing a substantially steplessvariable voltage comprising a helical winding, a paramagnetic coreextending through the Winding, a brush engageable only with part of aturn of the winding, means for moving the brush throughout a substantiallength of the Winding in slidable contact therewith, a closed Windingcomprising an annular paramagnetic core and a closed toroidal windingwound thereabout with the closed Winding encircling a portion of thecore and in spaced relation to the helical Winding, a second brush inslidable contact with said closed winding, means electrically connectingthe two brushes, input leads to the end portions of the helical winding,and an out put circuit including a lead to the closed winding and one ofthe input leads.

6. In combination with a variable transformer having a helical windingand a brush operable on the winding,

a brush actuating mechanism for moving the brush in a helical path toengage only one turn of the winding at 'a time comprising a membermounted for rotation about the axis of the winding, a screw rod carriedby the member and. extending along the longitudinal axis of the windingand having a pitch substantially equal to the pitch of the winding, abrush carrier formed with a threaded aperture through which the screwrod is threaded, means for rotating the member, means to maintain thescrew rod stationary on its longitudinal axis as it rotated about thewinding whereby the brush carrier is caused to move in a helical path incontact with only one turn of the winding at a time, and in which thereis a bushing positioned in the threaded aperture formed in the brushcarrier, said bushing having internal threads matching the threads onthe screw rod and external threads mating with threads formed on thebrush carrier, said external and internal threads having differentpitches to effectuate alignment of the brush carrier between the screwrod and the winding.

References Cited in the file of this patent UNITED STATES PATENTS2,773,966 Mastropole Dec. 11, 1956 2,785,261 Roberts Mar. 12, 1957FOREIGN PATENTS 740,520 Great Britain Nov. 16, 1955

